LCD devices have the advantages of portability, low power consumption, and low radiation, and because of this they have been widely used in various portable information products such as notebooks, personal digital assistants (PDAs), video cameras, and the like. Furthermore, LCD devices are considered to have the potential to completely replace CRT (cathode ray tube) monitors and televisions.
A transmissive LCD device displays images using light from a back light device, and is usable under any ambient light conditions. Because the transmissive LCD device requires a back light having high brightness, it has high power consumption. Further, the back light device can not be used for a long time.
Unlike the transmissive LCD device, a reflective LCD device utilizes ambient light beams from a natural light source or from an external artificial light source. The reflective LCD device can be used for a long time. However, the reflective LCD device is useless when the weather is unfavorable or when the external light source is not available.
To overcome the problems described above, a transflective LCD device has been developed. The transflective LCD device can compensate for the respective shortcomings of the reflective LCD device and the transmissive LCD device. That is, the transflective LCD device can selectively provide a reflective or transmissive mode, depending on the prevailing needs of users.
FIG. 7 is a schematic cross-sectional view of part of a conventional transflective LCD device 10. The transflective LCD device 10 includes a color filter substrate (not labeled), a thin film transistor (TFT) substrate (not labeled), and a liquid crystal layer 8 between the color filter substrate and the TFT substrate, and a back light module 18 disposed below the TFT substrate. The color filter substrate includes a first glass substrate 4, a color filter 5, a first electrode layer 6 and a first aligning film 7, formed in that order from top to bottom. The TFT substrate has a second aligning film 17, a second electrode layer 16, and a second glass substrate 14, formed in that order from top to bottom. The second electrode layer 16 defines a reflective region 161 and a transmission region 162, which is used for the LCD device 10 working in reflective mode and transmissive mode.
In the reflective mode, an ambient light ray from an external light source such as natural sunlight passes through the color filter 5, the first electrode layer 6, the first aligning film 7, the liquid crystal layer 8, the second aligning film 17 in that order, and is then reflected by the reflective region 161 of the second electrode layer 16 to pass back through the second aligning film 17, the liquid crystal layer 8, the first aligning film 7, the first electrode layer 6, and the color filter 5 in that order. That is the ambient light ray passes through the color filter 5 twice.
In the transmissive mode, light beams from the backlight module 18 transmit through the transmission region 162 of the second electrode layer 16, the second aligning film 17, the liquid crystal layer 8, the first aligning film 7, the first electrode layer 6, and the color filter 5 in that order. That is the ambient light ray passes through the color filter 5 once.
Because the light beams passes through the color filter 5 twice when the LCD device 10 works in the reflective mode, and the light beams passes through the color filter 5 once when the LCD device 10 works in the transmissive mode, the reflective mode has a better color purity than the transmissive mode in the transflective LCD device 10. That is, there is a difference in color purity as between the reflective mode and the transmissive mode.
What is needed, is an LCD device that can overcome the above-described deficiencies.